Before a drug is marketed: Clinical Trials
Phase 1, 2, and 3 studies each are designed to help researchers answer different questions.
Phase 1: represent the first studies in humans, and are designed to show whether the drug is safe, and how it behaves in the human body. These studies are usually conducted in healthy volunteers.
Phase 2: are intended to provide more detailed information about the safety of the drug, as well as an early glimpse into whether the drug has its intended effect in people with the target condition or illness.
Phase 3: are conducted in large numbers of people, once the drug is proven to be safe, and to work in a small number of people with the condition or illness. The investigational drug is usually compared with the current standard treatment
After a drug is approved: Registries
Different types of studies will be done after a drug has a license to be sold. These are commonly called Phase 4 studies, although Registries and Observational Studies can fall into this category as well.
The purpose of these studies is to gather additional information about the drug, often over a long period of time, in the real-world use of the drug by people with the condition for which the drug is intended to be used.